Preparation method of high-strength and high-conductivity nano hydrogel and hydrogel prepared by preparation method

Abstract

The invention belongs to the technical field of hydrogel high polymer materials, and particularly relates to a preparation method of high-strength and high-conductivity nano hydrogel and the hydrogel prepared by the preparation method. The preparation method of the hydrogel provided by the invention comprises the following steps: firstly, dissolving polyvinyl alcohol in a good solvent dimethyl sulfoxide of polyvinyl alcohol, and keeping an extended conformation and a staggered network; then, a poor solvent ethyl acetate of polyvinyl alcohol is introduced for non-solvent quenching, so that in-situ phase separation is promoted, polymer chains are drawn close, and interaction between the chains is enhanced; finally, neutral solvent water of polyvinyl alcohol is introduced for solvent replacement, the polymer microphase is evolved into nanofibers, and the polyvinyl alcohol hydrogel with nanoscale pores is formed. The hydrogel prepared by the invention has relatively high fracture stress strain and ionic conductivity, and effectively solves the problems of easy fracture, poor conductivity and the like of the traditional ionic thermoelectric gel.

Description

Technical Field

[0001] The present application relates to the technical field of hydrogel polymer materials, and more specifically, to a method for preparing a high-strength and high-conductivity nano-hydrogel and the hydrogel prepared therefrom. Background Art

[0002] Hydrogels are soft materials composed of a three-dimensional polymer network structure and a large amount of water. They possess high water absorption, biocompatibility, and tunable physical and chemical properties. They are widely used in fields such as biomedicine, environmental engineering, and flexible electronics. Their core characteristic lies in their ability to form a stable structure through cross-linking while maintaining a softness similar to that of biological tissue. Hydrogels are composed of hydrophilic polymer chains chemically or physically cross-linked to form a network structure. The interstices of hydrogels can accommodate over 60% water, which imparts excellent swelling and elasticity. Mechanical strength can also be adjusted by adjusting the cross-link density. Hydrogels are categorized into two types: natural (e.g., gelatin and chitosan) and synthetic (e.g., polyacrylamide and polyvinyl alcohol). Natural hydrogels have better biocompatibility, while synthetic materials offer advantages in mechanical properties and functional design.

[0003] With the rapid development of flexible electronics, wearable devices, and artificial intelligence technologies, smart sensors are showing great potential in health monitoring, human-computer interaction, soft robotics, and other fields. Hydrogel materials are widely used to develop a new generation of flexible sensors and smart devices due to their excellent flexibility, high water content, biocompatibility, and tunable ionic and electronic conductivity.

[0004] In the field of wearable sensors, hydrogels can be used as flexible electrodes, strain / pressure sensing units, and electrolyte interface materials, enabling real-time detection of skin and temperature signals. They possess mechanical compatibility and deformation compliance that are difficult to match with traditional metal or silicon-based materials. Furthermore, hydrogels maintain excellent electrical conductivity and structural integrity in scenarios such as complex surface fitting and dynamic stretching deformation, making them a key material for high-performance wearable systems.

[0005] Currently, most conductive hydrogels face a bottleneck in balancing mechanical and electrical properties. On the one hand, traditional hydrogels have poor mechanical strength and tensile strength, and are prone to microcracks or failure during repeated stretching or bending. On the other hand, the introduction of high loadings of conductive components (such as carbon nanotubes, metal nanowires, and conductive polymers) to enhance conductivity often compromises the structural integrity of the gel network, increasing brittleness and reducing interfacial adhesion, making them difficult to meet the demands of real-world applications in complex environments. Summary of the Invention

[0006] In order to solve the above technical problems, the present application provides a method for preparing high-strength and high-conductivity nanohydrogel and the hydrogel prepared therefrom. The obtained hydrogel material has high fracture stress and fracture strain, and can meet the stability of its own shape under deformation scenarios such as stretching and bending. At the same time, it has high ionic conductivity. When used to transmit electrical signals, it can solve the problems of poor mechanical properties and low ionic conductivity of traditional hydrogels.

[0007] In a first aspect, the present application provides a method for preparing high-strength and high-conductivity nano-hydrogels, using the following technical solutions: A method for preparing high-strength and high-conductivity nanohydrogel comprises the following steps: using polyvinyl alcohol as a raw material, dissolving it in a good solvent, gradually quenching it with a poor solvent, and performing solvent replacement with a neutral solvent to obtain an isotropic nanofiber hydrogel.

[0008] The specific steps include: (1) Pour polyvinyl alcohol powder into dimethyl sulfoxide, heat and mix, and then freeze the resulting solution to obtain polyvinyl alcohol organogel; (2) placing the polyvinyl alcohol organogel in ethyl acetate to obtain a polyvinyl alcohol-ethyl acetate gel; (3) The polyvinyl alcohol-ethyl acetate gel is placed in water to obtain a high-strength and high-conductivity nanohydrogel.

[0009] This application uses polyvinyl alcohol as the skeleton material, which has a high degree of alcoholysis, can ensure that a large number of hydroxyl groups are exposed and enhance interchain hydrogen bond crosslinking; dimethyl sulfoxide is used as a good solvent, and its strong polarity can destroy the hydrogen bonds between the polyvinyl alcohol chains, allowing the molecular chains to fully stretch. After being dissolved and frozen with polyvinyl alcohol, a pre-crosslinked organic gel is formed, laying a topological foundation for subsequent phase separation; ethyl acetate acts as a poor solvent to quench, ethyl acetate is miscible with dimethyl sulfoxide and repels polyvinyl alcohol, triggering instantaneous phase separation, forcing the polyvinyl alcohol chains to aggregate and shrink, and the interchain hydrogen bonds are quickly reconstructed at the phase interface to form a nanofiber prototype; water is used as a neutral replacement solvent, which can gradually replace ethyl acetate and dimethyl sulfoxide, retaining the nanostructure while introducing a hydrated environment, and constructing ion channels. The nanopores form a continuous water phase to achieve efficient ion transport.

[0010] More preferably, the polyvinyl alcohol has a degree of alcoholysis of 99% and a molecular weight of 146,000-168,000.

[0011] More preferably, the usage ratio of polyvinyl alcohol to dimethyl sulfoxide is 1 g:10 mL.

[0012] More preferably, the mixing temperature of the polyvinyl alcohol and dimethyl sulfoxide is 80° C., and the mixing time is 8-10 h.

[0013] Further preferably, the freezing temperature of the mixture of polyvinyl alcohol and dimethyl sulfoxide is -60°C, and the freezing time is 45-50 hours.

[0014] More preferably, the ethyl acetate concentration is 99.7%.

[0015] Further preferably, the mass ratio of ethyl acetate to polyvinyl alcohol organogel is greater than 100:1.

[0016] Further preferably, the mixing temperature of the ethyl acetate and the polyvinyl alcohol organogel is 15-30°C.

[0017] Further preferably, the polyvinyl alcohol organogel is allowed to stand in ethyl acetate for 20-26 hours.

[0018] Further preferably, the mixing temperature of the water and the polyvinyl alcohol-ethyl acetate gel is 15-30°C.

[0019] Further preferably, the polyvinyl alcohol-ethyl acetate gel is allowed to stand in water for 20-26 hours.

[0020] In a second aspect, the present application provides another method for preparing high-strength and high-conductivity nano-hydrogels, using the following technical solution: A method for preparing high-strength and high-conductivity nanohydrogels comprises the following steps: using polyvinyl alcohol as a raw material, dissolving it in a good solvent, gradually quenching it with poor solvents of different concentrations, and performing gradient solvent replacement with a neutral solvent to obtain isotropic nanofiber hydrogels.

[0021] The specific steps include: (1) Pour polyvinyl alcohol powder into dimethyl sulfoxide, heat and mix, and then freeze the resulting solution to obtain polyvinyl alcohol organogel.

[0022] (2) placing the polyvinyl alcohol organogel in ethyl acetate to obtain a polyvinyl alcohol-ethyl acetate gel.

[0023] (3) placing the polyvinyl alcohol-ethyl acetate gel in a 50 wt% ethyl acetate / water mixture, a 30 wt% ethyl acetate / water mixture, and a 10% ethyl acetate / water mixture, each time allowing to stand for 6-8 hours to obtain a preliminarily replaced hydrogel; (4) The hydrogel was placed in pure water and allowed to stand for 24 hours to obtain a high-strength and high-conductivity nanohydrogel.

[0024] When performing water replacement on polyvinyl alcohol-ethyl acetate gel, this application uses an ethyl acetate / water mixture and gradually reduces the concentration to induce mild phase separation, and finally replaces it with pure water. This can completely remove the ethyl acetate residue in the hydrogel, improve the internal pore connectivity of the hydrogel, and further enhance the conductive properties of the hydrogel.

[0025] In a third aspect, the present application provides a hydrogel, which adopts the following technical solution: A high-strength and high-conductivity nano-hydrogel is prepared by the above two preparation methods. The hydrogel forms a nanoscale pore network through non-solvent quenching and solvent replacement, and its mechanical strength and ion transport performance are significantly improved.

[0026] In summary, this application has the following beneficial effects: The present application provides a method for preparing a high-strength and high-conductivity nanohydrogel. The method comprises the following steps: first, dissolving polyvinyl alcohol in a good solvent, dimethyl sulfoxide, to maintain an extended conformation and an interlaced network; after quenching the polyvinyl alcohol by introducing ethyl acetate as a non-solvent for quenching the polyvinyl alcohol, the polyvinyl alcohol gel is subjected to in situ phase separation to bring the polymer chains closer together and enhance the interchain interactions; finally, the gel is solvent-exchanged with a neutral solvent, water, and the polymer microphases are transformed into nanofibers, thereby forming an isotropic nanoporous polyvinyl alcohol hydrogel.

[0027] Compared with the traditional freeze-thaw cycle method, this application uses a solvent step-by-step replacement strategy to regulate the phase separation behavior of polyvinyl alcohol at the molecular size, achieving the synergistic improvement of the mechanical / conductivity of pure polyvinyl alcohol hydrogel for the first time, solving the key material bottleneck of flexible electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron micrograph of the hydrogel prepared in Example 1 of the present application; Figure 2 This is a scanning electron microscope image of the hydrogel prepared in Comparative Example 1 of the present application; Figure 3 Graphs showing tensile stress-strain curves of the hydrogel (nf-gel) prepared in Example 1 of the present application and the hydrogel (c-gel) prepared in Comparative Example 1; Figure 4 The small-angle X-ray diffraction patterns of the hydrogel (nf-gel) prepared in Example 1 of the present application and the hydrogel (c-gel) prepared in Comparative Example 1; Figure 5 Ionic conductivity diagram of the hydrogel (NF-gel) prepared in Example 1 of the present application and the hydrogel (C-gel) prepared in Comparative Example 1 at different ion concentrations DETAILED DESCRIPTION

[0029] The following describes the embodiments of the present application through specific examples. Those skilled in the art can easily understand the other advantages and effects of the present application from the contents disclosed in this specification. The present application can also be implemented or applied through different specific embodiments, and the details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present application.

[0030] Furthermore, it should be understood that the mention of one or more method steps in this application does not preclude the presence of other method steps before or after the combination of steps, or the insertion of other method steps between these explicitly mentioned steps, unless otherwise stated. Furthermore, unless otherwise stated, the numbering of each method step is merely a convenient tool for identifying each method step, and is not intended to limit the order of the method steps or the scope of the application. Changes or adjustments to their relative relationships, without substantially changing the technical content, should also be considered within the scope of the application.

[0031] If the specific experimental conditions are not specified in the examples, they are usually based on conventional conditions in the field or conditions recommended by the reagent company; the materials, reagents, etc. used in the examples can be purchased through commercial channels unless otherwise specified.

[0032] The polyvinyl alcohol used in this application has a degree of alcoholysis of 99% and a molecular weight of 146,000-168,000. Example

[0033] Example 1 Preparation steps of high-strength and high-conductivity nano-hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 8 h, and then freeze the resulting solution at -60 °C for 48 h to obtain polyvinyl alcohol organogel.

[0034] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (105 times its mass) and allowed to stand at 25° C. for 24 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0035] (3) The polyvinyl alcohol-ethyl acetate gel was placed in deionized water 105 times its mass and allowed to stand for 24 hours to obtain a high-strength and high-conductivity nanohydrogel.

[0036] Example 2 Preparation steps of high-strength and high-conductivity nano-hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 8 h, and then freeze the resulting solution at -60 °C for 48 h to obtain polyvinyl alcohol organogel.

[0037] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (105 times its mass) and allowed to stand at 25° C. for 24 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0038] (3) The polyvinyl alcohol-ethyl acetate gel was placed in a 50 wt% ethyl acetate / water mixture, a 30 wt% ethyl acetate / water mixture, and a 10% ethyl acetate / water mixture in sequence, each time for 6 h, and then placed in deionized water for 24 h to obtain a high-strength and high-conductivity nanohydrogel.

[0039] Example 3 Preparation steps of high-strength and high-conductivity nano-hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 9 h, and then freeze the resulting solution at -60 °C for 45 h to obtain polyvinyl alcohol organogel.

[0040] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (105 times its mass) and allowed to stand at 25° C. for 20 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0041] (3) The polyvinyl alcohol-ethyl acetate gel is placed in deionized water and allowed to stand for 20 hours to obtain a high-strength and high-conductivity nanohydrogel.

[0042] Example 4 Preparation steps of high-strength and high-conductivity nano-hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 10 h, and then freeze the resulting solution at -60 °C for 50 h to obtain polyvinyl alcohol organogel.

[0043] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (105 times its mass) and allowed to stand at 25° C. for 26 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0044] (3) The polyvinyl alcohol-ethyl acetate gel is placed in deionized water and allowed to stand for 26 hours to obtain a high-strength and high-conductivity nanohydrogel.

[0045] Example 5 Preparation steps of high-strength and high-conductivity nano-hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 8 h, and then freeze the resulting solution at -60 °C for 48 h to obtain polyvinyl alcohol organogel.

[0046] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (110 times its mass) and allowed to stand at 25° C. for 24 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0047] (3) The polyvinyl alcohol-ethyl acetate gel is placed in deionized water and allowed to stand for 24 hours to obtain a high-strength and high-conductivity nanohydrogel.

[0048] Comparative Example Comparative Example 1 Preparation of hydrogel: 10g of polyvinyl alcohol powder was poured into 100ml of deionized water and stirred vigorously at 90°C until a uniform solution was formed. The solution was then poured into a mold and frozen in a -20°C refrigerator for 12 hours. It was then allowed to stand at room temperature for 6 hours. The freezing and room temperature standing operations were repeated three times to obtain a hydrogel prepared by the conventional freeze-thaw method.

[0049] Comparative Example 2 Preparation of hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of dimethyl sulfoxide, heat to 80 °C and stir for 8 h, and then freeze the resulting solution at -60 °C for 48 h to obtain polyvinyl alcohol organogel.

[0050] (2) The polyvinyl alcohol organogel is placed in ethanol with a mass 105 times that of the polyvinyl alcohol organogel and allowed to stand at 25° C. for 24 hours to obtain a polyvinyl alcohol-ethanol gel.

[0051] (3) The polyvinyl alcohol-ethanol gel is placed in deionized water and allowed to stand for 24 hours to obtain a hydrogel.

[0052] Comparative Example 3 Preparation of hydrogel: (1) Pour 10 g of polyvinyl alcohol powder into 100 mL of N,N-dimethylformamide, heat to 80 °C and stir for 8 h, then freeze the resulting solution at -60 °C for 48 h to obtain polyvinyl alcohol organogel.

[0053] (2) The polyvinyl alcohol organogel was placed in ethyl acetate (105 times its mass) and allowed to stand at 25° C. for 24 h to obtain a polyvinyl alcohol-ethyl acetate gel.

[0054] (3) The polyvinyl alcohol-ethyl acetate gel is placed in deionized water and allowed to stand for 24 hours to obtain a hydrogel.

[0055] Performance testing 1. The hydrogels prepared in Example 1 and Comparative Example 1 were subjected to scanning electron microscopy, mechanical properties, small-angle X-ray diffraction images, and ionic conductivity tests. The test methods are as follows: 1. Scanning electron microscope test The hydrogel samples prepared in Example 1 and Comparative Example 1 were respectively immersed in deionized water for 24 hours to reach a steady state, and then frozen in a -60°C low-temperature refrigerator for 3 hours, and then vacuum-frozen in a -30°C vacuum freeze dryer for 48 hours to remove moisture to obtain freeze-dried samples. Thereafter, the samples were fractured in liquid nitrogen, and the fractured cross-sections were subjected to gold spraying and the morphology was observed using a scanning electron microscope (Zeiss Ultra Plus Field Emission Scanning Electron Microscope).

[0056] 2. Mechanical properties test The hydrogel samples prepared in Example 1 and Comparative Example 1 were subjected to tensile testing using a 50N uniaxial stretching machine. The hydrogel strips used for the tensile test were dumbbell-shaped, with a rectangular stretching area measuring 20 mm x 2 mm x 1 mm. The uniaxial stretching speed was 50 mm / min. Tensile stress was calculated as: axial tension on the hydrogel / cross-sectional area of ​​the hydrogel × 100%. Tensile strain was calculated as: length of the hydrogel after stretching / length of the hydrogel before stretching × 100%.

[0057] 3. Small-angle X-ray diffraction image test The hydrogel samples prepared in Example 1 and Comparative Example 1 were respectively immersed in deionized water for 24 hours to reach a steady state, and then placed in a -60°C low-temperature refrigerator for 3 hours, and then placed in a -30°C vacuum freeze dryer for 48 hours to remove moisture to obtain freeze-dried samples. Thereafter, film samples were made and sent to a small-angle X-ray diffractometer for testing, and the X-ray wavelength was 0.15418 nm.

[0058] 4. Ionic conductivity test The hydrogel samples prepared in Example 1 and Comparative Example 1 were respectively immersed in deionized water for 24 hours to reach a steady state, and then immersed in potassium ferrocyanide / potassium ferrocyanide solutions with concentrations ranging from 0.1 mol / L to 0.4 mol / L for 24 hours to reach a steady state. Then, the ionic conductivity was tested using the AC impedance method function of an electrochemical workstation (Chenhua CHI660e) with an amplitude of 10 mV, and the start and end frequencies were 1 Hz and 10000 Hz, respectively.

[0059] The test results are shown in the attached Figure 1-5 ,Depend on Figure 1-5 It can be seen that the pores of the hydrogel prepared in Example 1 are about 100 nanometers, while the pores of the hydrogel prepared in Comparative Example 1 are about 100 micrometers. The pores of the hydrogel prepared in Example 1 are evenly distributed, while the pores of the hydrogel prepared in Comparative Example 1 are unevenly distributed.

[0060] 2. The maximum tensile stress and tensile strain of Example 1, Example 2, Comparative Example 2, and Comparative Example 3 were tested respectively, as well as the conductivity after immersion in a 0.3 mol / L potassium ferrocyanide / potassium ferrocyanide solution until steady state. The test results are recorded in Table 1 below.

[0061] Table 1 Test results By comparing the test results of Example 1 and Example 2, it can be seen that the conductivity of the hydrogel obtained by replacing the polyvinyl alcohol-ethyl acetate gel with ethyl acetate / water mixtures of different concentrations before replacing it with pure water is significantly improved. This is because the replacement with ethyl acetate / water mixture first can induce mild phase separation of the gel, and combined with pure water replacement, the residual ethyl acetate and dimethyl sulfoxide in the hydrogel can be completely removed, thereby improving the internal pore connectivity of the hydrogel and further improving the conductivity of the hydrogel. The complete removal of organic solvents is beneficial to applications in fields such as wearable devices that are in direct contact with the human body.

[0062] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form or substance. It should be pointed out that ordinary technicians in this technical field can make several improvements and supplements without departing from the method of the present invention. These improvements and supplements should also be regarded as the scope of protection of the present invention. Any equivalent changes, modifications and evolutions made by technicians familiar with this profession without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments based on the essential technology of the present invention are still within the scope of the technical solution of the present invention.

Claims

1. A method for preparing high-strength and high-conductivity nano-hydrogel, characterized in that: The steps include: (1) Pour polyvinyl alcohol powder into dimethyl sulfoxide, mix and stir, and then freeze the resulting solution to obtain polyvinyl alcohol organogel; (2) placing the polyvinyl alcohol organogel in ethyl acetate to obtain a polyvinyl alcohol-ethyl acetate gel; (3) The polyvinyl alcohol-ethyl acetate gel is placed in water to obtain a high-strength and high-conductivity nanohydrogel.

2. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The polyvinyl alcohol has an alcoholysis degree of 99% and a molecular weight of 146,000-168,000.

3. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The usage ratio of the polyvinyl alcohol to dimethyl sulfoxide is 1 g:10 mL.

4. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The mixing temperature of the polyvinyl alcohol and dimethyl sulfoxide is 80° C., and the mixing time is 8-10 hours.

5. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The freezing temperature of the polyvinyl alcohol and dimethyl sulfoxide after mixing is -60°C, and the freezing time is 45-50 hours.

6. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The mass ratio of the ethyl acetate to the polyvinyl alcohol organogel is greater than 100:

1.

7. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: The mixing temperature of the ethyl acetate and the polyvinyl alcohol organogel is 15-30° C., and the standing time of the polyvinyl alcohol organogel in the ethyl acetate is 20-26 hours.

8. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 1, characterized in that: In step (3), before being placed in water, the polyvinyl alcohol-ethyl acetate gel is sequentially placed in a 50 wt% ethyl acetate / water mixture, a 30 wt% ethyl acetate / water mixture, and a 10% ethyl acetate / water mixture for treatment, each time being allowed to stand for 6-8 h.

9. The method for preparing high-strength and high-conductivity nano-hydrogel according to claim 8, characterized in that: The mixing temperature of the water and the polyvinyl alcohol-ethyl acetate gel is 15-30° C., and the polyvinyl alcohol-ethyl acetate gel is allowed to stand in water for 20-26 hours.

10. A high-strength and high-conductivity nano-hydrogel, characterized in that: The high-strength and high-conductivity nano-hydrogel is prepared by the preparation method according to any one of claims 1 to 9.

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